Photochemical synthesis and stereochemistry of cobalt(III) complexes containing 2-thiouracilate and related ligands

Abstract

Eight cobalt(III) complexes containing four-membered N,S chelates [CoL(en)₂]⁺ and [Co(HL)(en)₂]²⁺{H₂L = 2-thiouracil [2,3-dihydro-2-thioxo-(1H)-pyrimidin-4-one](H₂tuc), 5-methyl-2-thiouracil (5Me-H₂tuc), 6-methyl-2-thiouracil (6Me-H₂tuc) or 2,3-dihydro-2-thioxo-(1H)-quinazolin-4-one (H₂quz); en = ethane-1,2-diamine} have been photochemically prepared from robust [Co(en)₃]Cl₃ and the ligands in moderate yields and characterized by elemental analyses, UV/VIS absorption and NMR spectroscopy. The crystal structure of [Co(tuc)(en)₂]ClO₄·H₂O was determined from 3905 reflections to R= 0.053 (R′= 0.056): space group P(triclinic) with a= 9.489(2), b= 10.968(2), c= 8.640(2)Å, α= 101.28(2), β= 115.19(1), γ= 80.61(2)° and Z= 2. The tuc ligand co-ordinates through N and S donors and the complex adopts an adjacent linkage form where the C⁴ oxygen atom is located near the en chelate ring. A characteristic intramolecular hydrogen bond N–H ⋯ O [N ⋯ O 2.876(8)Å and N–H ⋯ O 143.14°] was found between the oxygen atom of the tuc and an amine proton of en, which contributes to the stabilization of the sterically unfavourable adjacent isomer. Proton NMR spectroscopy showed that the hydrogen bond is also present in D₂O and (CD₃)₂SO solutions.